The present invention relates generally to medical devices and, in particular, aortic cannulas. Aortic cannulas are used to return blood to the aorta while the heart is by-passed during heart surgery. These cannulas are purposely made with small diameters to minimize disruption to the aorta, which in many heart surgery patients have advanced complex atherosclerotic plaque with adherent blood from bithrombi. Some conventional cannulas have a single discharge opening for the blood. It is desirable to eliminate or minimize impact onto the aortic wall of the blood exiting the cannula.
Aortic cannulas generally comprise an elongated tube having a terminal end. In at least some styles of conventional cannulas, a single opening is provided in the terminal end which provides a single stream of blood exiting the cannula and entering the aortic arch. Due to the small diameter of the cannula, the flow velocity of the blood through the single opening in the terminal end of the cannula is extremely high resulting in "jet" flow. The fluid pressure at the discharge end of the prior art cannula is also high. It is believed that the force of this jet stream of blood dislodges atherosclerotic plaque and/or adherent thrombi from the walls of the aorta, causing embolisms and strokes.
Attempts in the art to prevent embolisms resulting from cannulation have included designing the cannula in order to reduce the velocity of blood exiting the terminal end. For instance, U.S. Pat. No. 5,354,288 describes a cannula having a conical diffuser placed toward the proximal end of the cannula. The cannula includes several outlet openings in the sidewall to permit blood deflected by the diffuser to flow out of the cannula. This cannula design, however, still directs blood toward the sides of the aortic arch wherein the atherosclerotic plaque usual lies. Thus, the patient is still susceptible to embolisms and strokes.
Therefore, a primary objective of the present invention is the provision of an improved aortic cannula which disperses blood into the aorta with little, if any, contact on the aortic wall.
Another objective of the present invention is the provision of an improved aortic cannula having a spoon-shaped discharge lip to prevent impact of exiting blood on the aortic wall.
Another objective of the present invention is a provision of an improved aortic cannula which has an internal bead adjacent the terminal end to facilitate blood dispersion from the cannula.
Another objective of the present invention is a cannula which discharges the blood in a U-shaped stream.
Another objective of the present invention is a cannula which discharges the blood in a direction centrally aligned with the aortic lumen so as to avoid or minimize impact on the aortic wall.
A further objective of the present invention is the provision of an improved aortic cannula having a discharge opening with an upper end having an inverted V-shaped contour to facilitate dispersion of blood from the cannula.
These and other objectives will become apparent from the following description of the invention.